Role of rheological properties on physical chitosan aerogels obtained by supercritical drying.

Chitosan aerogels were obtained after using supercritical carbon dioxide to dry physical hydrogels, studying the effect of the rheological behavior of hydrogels and solutions on the final aerogels properties. An increase on the solutions pseudoplasticity increased the subsequent hydrogels physical entanglement, without showing a significant effect on aerogels morphology (nanoporous) and textural properties (pores of about 10 nm). However, an increase of hydrogel physical entanglement promoted the formation of aerogels with a higher compressive strength (from 0.2 to 0.80 MPa) and higher thermal decomposition range, while decreasing the porosity (from 90 % to 94 %). Aerogels stress-strain responses were also successfully fitted using a hyperelastic equation with three adjustable parameters (Yeoh), showing that this type of models must be taken into account when large stresses are studied.

Palladium(II)-Catalyzed Intramolecular C-H Alkenylation for the Synthesis of Chromanes.

The intramolecular Pd(II)-catalyzed alkenylation of aryl homoallyl ethers constitutes a mild, versatile, and efficient procedure for the synthesis of highly and diversely substituted chromanes and 2 H-chromenes. The use of p-TsOH as an additive allows more efficient reactions that could be carried out a room temperature in most cases. The procedure has a wide scope, allowing the synthesis of alkylidenechromanes and 2 H-chromenes substituted at C-2 or C-3 of the chromene moiety, thus accessing relevant flavenes and isoflavenes, and even coumarins, in high yields (59 to 91%, 32 examples).